1. Field of the Invention
The present invention generally relates to increasing the throughput of scanning lithography systems, and more particularly to a rotational mask scanning method and apparatus for increasing the throughput of such systems.
2. Description of the Related Art
Overlay and image size specifications continue to decrease at a rapid pace driving the migration from traditional step and repeat exposure tools to scanning systems which have improved optical subsystems. However, while the improved optics of the scanning systems may meet the more rigorous specifications, the throughput of these systems is nonoptimal which increases the operation costs.
Conventional translational scanning masks utilize considerable amounts of time stopping and starting. After each field is printed, a reticle of a scanning system must be stopped, repositioned, and accelerated to the selected scanning speed. As a result, considerable mass reduction design constraints are placed on the reticle and reticle stage.
Thus, even though the traditional translational masks utilize very high acceleration/deceleration and scanning speeds to maximize the time spent exposing the wafer, considerable time is still lost in stopping and starting, as mentioned above. As a result, this greatly reduces the throughput of the scanning systems and increases the complexity and cost of the reticle stage.
Furthermore, fundamental throughput limits are being reached due to the increasing percentage of time spent on overhead tasks (e.g., stopping, starting, aligning, etc.) as opposed to time spent exposing the wafer. The conventional systems do not allow for future throughput improvements as wafer stage speed and laser power increases.
In view of the foregoing and other problems of the conventional methods and systems, an object of the present invention is to provide a structure and method for improving throughput and for simplifying reticle handling.
Yet another object is to provide for continuous scanning across a wafer without having to stop or start the mask or wafer.
A still further object is to optimize efficiency by designing the rotational mask size to match the printed field size.
In a first aspect of the present invention, a photo-exposure tool for exposing a plurality of images on a workpiece, includes a rotatable mask having a pattern of image segments thereon, an optical system for projecting the image segments onto the workpiece, and a device for at least one of rotating the mask and for moving the workpiece so as to continuously expose a plurality of regions on the workpiece with the pattern of image segments.
Thus, with the inventive method and system, throughput is optimized and operation costs are reduced as compared to the conventional methods and systems.
Moreover, the present invention provides a rotational mask which allows for continuous printing of fields without constant starting and stopping. Therefore, higher overall throughput, flexibility in design, and less frequent acceleration/deceleration are achieved.
Furthermore, the inventive structure allows for future throughput improvements as wafer stage speed and laser power increases.